# -*- coding: utf-8 -*-
"""
Spyder Editor

This is a temporary script file.
"""
            
#(百分制成绩转化为等级制成绩)
x = float(input("0-100:"))
if x >= 90:
     y = "A" 
elif x > 80 and x < 90:
     y = "B"
elif x > 70 and x < 80:
     y = "C"
elif x > 60 and x < 70:
     y = "D"
elif x < 60:
     y = "E"
print("等级制成绩为:y")

"""
#计算三角形的面积
 """
 #三角形的三边长:
 
a = float(input("a = :"))
b = float(input("b = :"))
c = float(input("c = :"))

if a + b > c and b + c > a and a + c > b:
    p = (a + b + c)/2
    area = (p * (p - a) * (p - b) * (p - c)) ** 0.5
    print("三角形的面积是：%.3f" % area)